一个新的水稻联会复合体中央元件蛋白的分离及其功能研究

For all sexually propagating eukaryotes, meiosis is the crucial process of producing haploid gametes and consists of two rounds of chromosome division following a single round of DNA replication. In meiosis, the normal crossover recombination requires both homologous chromosome pairing and synaptonemal complex (SC) assembly. The SC mediates the intimate association of homologous chromosomes along their entire lengths following the initial homologous alignment and promotes the post-homology search steps in meiotic recombination. The SC is a zipper-like structure in which the lateral elements constitute the two parallel backbones and the transverse filaments (TFs) are similar to the teeth of the zipper. The region where the TF teeth meet and interdigitate is the central element (CE), corresponding to the electron-dense structure running along and between the two parallel LEs in electron microscopy examination. Studies in mice and Drosophila have identified several proteins specifically localizing to the SC central element. These non-TF central region proteins show poor conservation among species and are essential for the TF assembly within SCs. In our previous study, one asynaptic mutant, sce1, induced by 60Co γ-ray irradiation was collected from rice plants. And one candidate gene, SCE1, was identified by map-based cloning. SCE1 encodes a protein with 475 amino acids, which is a novel protein in eukaryocytes. To investigate the spatial and temporal localization of SCE1, a polyclonal antibody was raised against the full-length SCE1 protein. SCE1 first appeared as punctuate foci on chromosomes at leptotene. At early pachytene, SCE1 was observed as linear signals along the entire chromosome axes. At late pachytene, when REC8 was present as double thread signals on chromosomes, the SCE1 signals were situated in the center between and along the REC8 signals, indicating that SCE1 localizes to the SC central region. In this proposal, we are going to strength our knowledge on the biological functions of SCs by characterizing the roles of SCE1 during rice meiosis. Our research will be focused on the following aspects: (1) to explore the possibility and mechanism that SCE1 involved in meiotic DSB formation; (2) to reveal the direct interaction between SCE1 and the TF protein, ZEP1; (3) to study the possible pathway and interactions among different elements of rice SCs. We believe that those findings will contribute a great deal to our understanding of rice meiosis, especially for biological functions of the synaptonemal complex.

减数分裂过程中，同源染色体配对与联会复合体形成，是极其复杂而又关键的生物学过程。充分认识这一生物学过程，揭示其基因作用网络，将有助于实现对减数分裂的遗传调控。我们获得了一减数分裂不联会突变体sce1，并初步完成突变基因的图位克隆。候选基因SCE1编码一含有475个氨基酸的功能未知蛋白。免疫荧光定位表明，SCE1位于联会复合体的中央，很可能是植物中发现的第一个联会复合体中央元件组分。本课题拟在前期研究基础上，通过对SCE1功能的深入研究，明确SCE1是如何参与DSB的形成和介导同源染色体配对的；解析SCE1是如何与横丝蛋白ZEP1互作，组装成联会复合体的；阐明SCE1参与联会复合体形成的作用网络。研究结果不仅对水稻联会复合体的组装与调控有重要认识，同时将对整个减数分裂分子机理的解析增加新的思路。

在减数分裂过程中，同源重组能够引起遗传物质在同源染色体间进行交换，是生物多样性形成的主要原因之一。同时，同源重组最终形成的交叉结介导染色体的均等分离，确保了遗传物质的稳定遗传。联会复合体通过介导同源染色体的联会，进而促进同源重组的正常进行。在粮食作物水稻中，对联会复合体组成原件的鉴定和基因互作网络的揭示，将有助于实现对减数分裂的遗传调控以至于育种应用。本项目在前期研究基础上，对水稻中一个新的联会复合体组分OsSDS(SCE1)进行了鉴定，并对OsSDS如何在同源重组中发挥功能进行了研究。免疫荧光定位研究表明，OsSDS与联会复合体横向细丝蛋白ZEP1共定位于联会复合体的中央区，并且两者的定位相互依赖。在Ossds突变体中，同源染色体不配对，DSB形成标记γH2AX的信号消失，且Ossds可以抑制Osrad51c的突变表型；Ossds突变体中，染色体轴能形成正常，但联会复合体（SC）中央元件的组装不能正常完成；OsSDS 是OsMSH5，OsMER3和OsZIP4在染色体上定位的关键。以上结果说明OsSDS作为一个同源重组起始因子参与同源重组的调控。在SCI收录核心期刊发表基金标注论文5篇，申请国家专利一项。培养博士硕士研究生4人，博士后1人，青年教师晋升2人。研究结果不仅鉴定了一个新的水稻联会复合体成员，同时对水稻联会复合体的组装与调控有了进一步的认识。